x-ray imaging (0.1 arcsec at 6.7 kev) and hxr polarimetry (10 – 50 kev)

X-Ray Imaging (0.1 arcsec at 6.7 keV)

andHXR Polarimetry

(10 – 50 keV)

Brian DennisNASA/GSFC

G.K.Skinner

Zone Plate Phase Zone Plate Phase Fresnel Lens

10.1% 40.4% 100%

Focusing X-rays

Phase Fresnel Lens

Focal length is a function of photon energy

DEM = 0.36 1049 (T/2keV)-0.72 cm-3 keV-1

Fe abundance = 2.0 x photosphericCa – 4.7 x photosphericS – 0.4 x coronalSi – 0.2 x coronal

1 2 4 6 8

GOES M2.8 Flare

Phase Fresnel Lens – a possible design concept

50-100 m boomor

formation flying

CCD array(s)eg 100 mm

Fresnel lens(es)or PZPs eg 1-2 cm dia

CCD arrayeg 100 mm

Fresnel lensor PZPs eg 1-2 cm dia

Angular resolution ~ 0.1 arc secField of view ~ few arc minsEffective area ~ 1 cm2 (in a line)

Hard X-ray Imaging Polarimetry• Energy range ~2 – ~50 keV

– Complements Compton scattering polarimetry >50 keV

• Photoelectron track imaging– Time Projection Chamber (TPC)

• Goddard development– Gas Electron Multiplier (GEM) with strip readout– 70%/30% mixture of argon and dimethyl ether (DME)– 2-D positional information – strip number & time– Modulation collimators for Fourier-transform imaging– Leverage off GEMS SMEX for astrophysics

• Italians developing direct 2-D capability– Focusing optics for direct imaging polarimetry

Time Projection ChamberPolarimeter

Effective Area vs. Energy

Time Projection Chamber

Imaging Polarimeter Concept

100 cm

Bi-g

rid

R

MC

Fill

/p

um

p

Drift electrode

10 cm

30 cm

GEM

Readout anodeX-r

ay

win

do

w

Inci

de

nt

X-r

ays

100 cm

Bi-g

rid

R

MC

Fill

/p

um

p

Drift electrode

10 cm

30 cm

GEM

Readout anodeX-r

ay

win

do

w

Inci

de

nt

X-r

ays

The End

Lens Parametersto focus 6.7 keV X-rays

Lens material Silicon

Focal length 90 m

Aperture diameter 2 cm

Finest pitch 1.7 μm

Profile height 8.4 μm

Base thickness <5 μm

X-ray Imaging RequirementsUnits Notes

Lens – detector requirements

Lens –detector separation 80-100 m

Pixel size for 0.1” resolution 25 microns X-ray CCD array or X-ray pixel detector

Field of view 3 arc min Assumes 10 cm detector to cover a typical active region - could be larger.

Station keeping requirements

Control - transverse 2 cm Requirement is to keep image on detector – could move detector or lens independently.

Control – axial 25 cm Not critical; 25 cm is equivalent to 20 eV energy shift

Knowledge - transverse <0.1 arc sec Alignment of line joining lens and detector must be known relative to the Sun direction to an accuracy better than the desired resolution, equivalent to 25 microns at 100 m

Knowledge – axial 10 cm Not critical

Attitude requirement 10 arc min Tilt and tip of lens and detector are not critical